Very high QP eigenvalue for lowest orbital

Concerns issues with computing quasiparticle corrections to the DFT eigenvalues - i.e., the self-energy within the GW approximation (-g n), or considering the Hartree-Fock exchange only (-x)

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subhayan
Posts: 32
Joined: Thu Sep 26, 2019 7:48 am

Very high QP eigenvalue for lowest orbital

Post by subhayan » Mon Dec 06, 2021 10:49 pm

Dear developer,

I am trying to run a BSE calculation on a slightly distorted (actually from a molecular-dynamics snapshot) methanol molecule. However, I am getting negative excitation energies for the first two excitations. I guess this has to do with the fact that, in the output of the GW calculation, I am getting E-Eo= 21.49 (Eo=-20.33 , E=1.16) for the first quasiparticle orbital. Could you kindly take a look at the attached files and let me know your thoughts?

For the GW calculation: the input is GW_input.in and the output is r_em1d_ppa_HF_and_locXC_gw0_rim_cut
For the BSE calculation: the input is 02_BSE_construct_solve.in and the output is r-3D_BSE_optics_bse_bss_dipoles_em1s_rim_cut

Kindly let me know if you need any other files.

Best regards,
Subhayan
MethanolYambo.tar.bz2
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Subhayan Roychoudhury
Postdoctoral researcher
Lawrence Berkeley National Laboratory

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Daniele Varsano
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Joined: Tue Mar 17, 2009 2:23 pm
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Re: Very high QP eigenvalue for lowest orbital

Post by Daniele Varsano » Tue Dec 07, 2021 8:12 am

Dear Subhayan,
yes, the problem is that the QP energy of the first deep state is not calculated properly. The problem is the Z factor:

Code: Select all

B=1 Eo=-20.33 E=  1.16 E-Eo= 21.49 Re(Z)=**** Im(Z)= -2.05918 nlXC=-31.45032 lXC=-19.44300 So=  7.05307
It would be possible to investigate it, e.g. some instability in the self-energy derivative for this deep state, but it is not straightforward, you could see for instance the effect
of reducing the dScStep variable.

Anyway, I think that it is not relevant to include such a deep state in the BSE and I would remove the first states from the BSEBands.

Please also check your CUTRadius that seems a bit small.

Best,
Daniele
Dr. Daniele Varsano
S3-CNR Institute of Nanoscience and MaX Center, Italy
MaX - Materials design at the Exascale
http://www.nano.cnr.it
http://www.max-centre.eu/

subhayan
Posts: 32
Joined: Thu Sep 26, 2019 7:48 am

Re: Very high QP eigenvalue for lowest orbital

Post by subhayan » Tue Dec 07, 2021 10:19 am

Perfect. Thanks a lot :-)
Subhayan Roychoudhury
Postdoctoral researcher
Lawrence Berkeley National Laboratory

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